A belt type continuously variable transmission (to be referred to as a “CVT” hereafter) comprises a pair of pulleys having a variable groove width and a belt wrapped around the pulleys, and is capable of varying a speed ratio continuously by modifying the respective groove widths of the pulleys. In a vehicle installed with a CVT, an engine can be used in a more efficient operating condition than in a vehicle having a conventional stepped transmission, and therefore improvements in a power performance and a fuel consumption performance of the vehicle can be expected.
To improve the power performance and fuel consumption performance of a vehicle installed with a CVT further, a speed ratio range (to be referred to as a “ratio range” hereafter) of the CVT is preferably enlarged. By enlarging the ratio range of the CVT, speed ratios on a large speed ratio side can be used during startup and acceleration, thereby further improving the power performance of the vehicle, and speed ratios on a small speed ratio side can be used during high-speed travel, thereby further improving the fuel consumption performance of the vehicle.
To enlarge the ratio range of the CVT, a pulley diameter may be increased, but with this method, the CVT increases in size and weight, which is undesirable.
Therefore, in JP60-37455A and JP61-241561A, a two-forward speed subtransmission mechanism is provided in series with the CVT to the front or rear thereof, and by changing a gear position of the subtransmission mechanism in accordance with the operating conditions of the vehicle, a wide ratio range is realized without increasing the size of the CVT.